In air or vacuum planters wherein a rotating disc with seed pockets is used to singulate kernels of grain, such as shown in U.S. Pat. Nos. 1,046,199; 1,331,235; 2,991,909; 3,434,437; 3,608,787 and 3,888,387; it is desirable to adequately seal the pressure or vacuum chamber in relation to the atmosphere. The present invention has that objective.